As is well known, there exists a vehicle power source system provided with two electric storage devices having different voltages. There will be considered the case where in such a vehicle power source system, a high-voltage electric storage device out of the two electric storage devices fails. In the case where the high-voltage electric storage device fails, it is required to cut off charging and discharging currents for the high-voltage electric storage device so as to prevent the charging and discharging currents from providing an adverse effect to other devices and circuits. That is to say, for example, in the case where the high-voltage electric storage device is formed of a lithium ion battery and the lithium ion battery fails, excessive charging or abnormal heat generation may cause smoke or fire; therefore, the charging and discharging currents need to be cut off as soon as possible. Thus, when the high-voltage electric storage device fails, a current cutoff mechanism (e.g., a relay) cuts off the charging and discharging currents for the high-voltage electric storage device.
However, even when the high-voltage electric storage device fails and hence the charging and discharging currents therefor is cut off, it is required to make the vehicle travel to and stop in a safe place, i.e., a limb-home function is required; for the purpose of obtaining the limb-home function, it is required to continue or restart the power generation. In this situation, for example, in the case of a vehicle power source system in which the electric power generator is an AC power generator that has a magnetic-field winding and is driven by rotation power of an internal combustion engine or the like so as to generate AC electric power and a high-voltage electric storage device supplies electric power to the magnetic-field winding by way of a magnetic-field circuit, it is not made possible to supply electric power to the magnetic-field circuit so as to continue or restart the electric-power generation, when the high-voltage electric storage device is shut down. To date, in order to solve the foregoing problems, technologies disclosed, for example, in Patent Documents 1 through 4 have been proposed.
That is to say, Patent Document 1 discloses a technology in which there are provided two electric storage devices as a main power source and a subsidiary power source having different voltages, a first power supply circuit that connects the subsidiary power source with the main power source and general loads by way of a DC/DC converter, a second power supply circuit that is in parallel with the first power supply circuit and connects the subsidiary power source with the main power source and general loads by way of a switch, and a control means that controls the operations of the DC/DC converter and the switch and in which there is selected any one of a first control state where the DC/DC converter is activated and the switch is opened and a second control state where the DC/DC converter is stopped and the switch is closed. This technology makes it possible that when the subsidiary power source fails and is shut down, the first power supply circuit is disconnected and the second power supply circuit is connected so that electric power is supplied from the main power source to the magnetic-field circuit.
Patent Document 2 discloses a technology in which there are provided two electric storage devices having different voltages, an electric power generator including a rotor having a magnetic-field coil and a stator having an armature coil, a rectifier that rectifies AC electric power generated across the armature coil, an excitation control circuit that controls a voltage to be supplied to the magnetic-field coil, a capacitor that is connected to the DC side of the rectifier and receives and supplies electric power, a battery connected with a load, a DC/DC converter that is connected between the capacitor and the battery and can convert a unilaterally or bilaterally inputted DC voltage into an arbitrary voltage, and a selection switch that can select the capacitor or the battery as a power supplying source for the excitation control circuit. This technology makes it possible that when the capacitor fails and is cut off, the selection switch is switched over to the battery side so that electric power is supplied from the battery to the excitation control circuit.
Moreover, Patent Document 3 discloses a technology in which there are provided two electric storage devices having different voltages, an AC/DC converter unit that converts an AC voltage into a DC voltage, a smoothing capacitor connected with the DC side of the AC/DC converter unit, a DC/DC converter unit that has a semiconductor switch and applies DC/DC conversion to DC electric power across the smoothing capacitor so as to supply the DC electric power to a load, and a control device that, while controlling the AC power factor, controls the AC/DC converter unit so that the DC voltage of the AC/DC converter unit follows a target value and concurrently controls the DC/DC converter unit through duty control of the semiconductor switch so that a DC input or output between the DC/DC converter unit and the load follows a command value and in which when the duty ratio of the semiconductor switch is 100□, the semiconductor is always on, so that when the voltage drops in the semiconductor and the smoothing reactor are neglected, the output voltage of the DC/DC converter unit becomes equal to the output voltage (the voltage across the smoothing capacitor). This technology enables the input and output sides of the DC/DC converter to communicate with each other; thus, it is made possible that when the high-voltage electric storage device is shut down, the input and output sides of the DC/DC converter are made to communicate with each other so that electric power is supplied from the low-voltage electric storage device to the magnetic-field circuit.
Patent Document 4 discloses a technology for a vehicle power source apparatus in which there are provided a first electric storage device, a second electric storage device that is charged and discharged at a voltage lower than the voltage of the first electric storage device, an inverter circuit that receives a voltage from the first electric storage device by way of an opening/closing switch, a smoothing capacitor provided in parallel with and between the first electric storage device and the inverter circuit, a DC/DC converter that is provided between the smoothing capacitor and the second electric storage device, applies voltage conversion to electric energy stored in the first electric storage device or the smoothing capacitor so as to supply the converted electric energy to the second electric storage device, and applies voltage conversion to electric energy stored in the second electric storage device so as to supply the converted electric energy to the smoothing capacitor, and an electronic control unit that controls the DC/DC converter, before the inverter circuit is energized, so as to charge the smoothing capacitor up to a voltage that is within a predetermine allowable voltage range of the storage voltage of the first electric storage device and then close the opening/closing switch, in which the DC/DC converter is provided with a step-down switching circuit connected with the smoothing capacitor, a step-up switching circuit connected with the second electric storage device, and a transformer provide between the step-down switching circuit and the step-up switching circuit, steps up a voltage from the second electric storage device so as to supply the stepped-up voltage to the smoothing capacitor, when the control by the electronic control unit switching-drives the step-up switching circuit, and steps down a voltage supplied from the first electric storage device by way of the opening/closing switch so as to supply the stepped-down voltage to the second electric storage device, when the control by the electronic control unit switching-drives the step-down switching circuit, and in which when the voltage applied to the smoothing capacitor becomes higher than the output voltage of the first electric storage device, the electronic control unit stops the switching driving of the step-up switching circuit and then activates the step-down switching circuit.